Diagnostics
- Make
- MG
- Model
- MGF Stepspeed EM-CVT Automatic Gearbox Workbook
- Section
- Diagnostics
The most serious fault will cause the transmission to be stuck in a single gear ratio. If stuck in the lowest gear, the driver will see the engine speed quickly increase to 6000 rpm and stay there. The maximum possible vehicle speed is approximately 30 mph. If stuck in the highest gear, the driver will experience very sluggish acceleration and engine speeds hanging around 2000 to 2250 rpm at vehicle speeds of up to 50 mph.
Diagnostics
All diagnostics of the Em-CVT are carried out via the EMS. Using TestBook, the EMS can request actions from the GIU and monitor these actions for the correct performance.
A requirement has been identified for the GIU to perform an integrity check on its output drives. This mode will be engaged as part of the end of line testing during production, and also for the technician performing diagnostic testing. In response to these signals, the GIU shall perform the following:
- Perform a test on the LED drives
- Test the shift lock solenoid drive, if fitted
- Attempt to move the motor through a complete cycle
Fault finding
Once the operation of the MEMS 3 has been established, GIU operation should be established. The serial link between the GIU and the EMS can be verified by observing the LCD display in the instrument pack. The display should change in accordance with the gear lever selector and is an indication that the selector switches are operational and the drive from the EMS to the instrument pack is operational.
Possible causes of transmission faults are described in the 'Fault table'.
Fault table
| Fault /symptom | Possible causes |
|---|---|
| Transmission stays in highest ratio: Vehicle pulls away as normal but engine speed does not rise as normal. | • Faulty road speed sensor • Interference on road speed sensor • Faulty throttle potentiometer • Ratio control motor fault |
| Vehicle pulls away and accelerates sluggishly | • Transmission malfunction |
| Transmission stays in lowest ratio: Vehicle pulls away as normal but engine speed rises rapidly and reads approximately 6000rpm at 30kph | • Sticking primary valve • Ratio control motor fault • Ratio control motor wiring fault affecting phases • Transmission malfunction |
| Engine speed stuck at 3000rpm: The ratio control motor is permanently at step 130. This is the default mode for the transmission, protecting it from damage | • Selector switch fault • Link lost between ECM and GIU • Ratio control motor fault • Speed sensor fault |
| No centre console LED illumination with ignition on | • Short circuit. If the GIU detects a short circuit in the LED module it will extinguish all LED's • Open circuit between GIU and selector connector • GIU fault • Invalid selector switch combination /selector fault |
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